Helmbrecht 2018

Helmbrecht, T. O., dal Maschio, M., Donovan, J. C., Koutsouli, S., & Baier, H. (2018). Topography of a Visuomotor Transformation. Neuron.

In ZF, two distinct pathways from OT to HB: one for prey, another for avoidance. Rev: damage to OT prevents orienting towards prey. Optogenetics: stimulate diff neurons in the OT, detect motor outputs. Clustering: 2 distinct behav: escapes and approaches. Moreover, retinotopic position and eye position are integrated, to calculate the maneuver. Combined with whole-brain gcamp img, observed targeted HB neurons activated. Then traced individ neurons and classified into 8 classes, based on projection targets, including ipsi- and contra- to HB, several distinct type of commissural, etc. Up-down retinotopy is less precisely encoded than LR (aka rostro-caudal).

Abbas 2017

Abbas, F., Triplett, M. A., Goodhill, G. J., & Meyer, M. P. (2017). A Three-Layer Network Model of Direction Selective Circuits in the Optic Tectum. Frontiers in neural circuits, 11, 88.

[Abbas 2017] Define 3 layers as: axons of RGCs, supervisial inhibitory interneurons (SIN), and principal or paraventricular neurons (PVN). ZF larvae. Claim that at first 2 levels there are only 3 principal directions (a trifoil, equally split), but they get recalculated into 4 at last layer (rostro-caudal is absent in the RGCs input, but is present in OT). In intro: there seems to be a controversy in ZF, about how exactly inhibition is tuned in direction-selective circuits in the OT, and whether it is sharpening, or defining the responses. Model: just 10 neurons, as each one represents an entire population; 3 layers, ReLU units, diff equations (not too discrete). Custom set input sensitivity curves and tuned connectivity scheme, reproduces tuning from Ca img experiments

Thompson 2016

Thompson, A. W., Vanwalleghem, G. C., Heap, L. A., & Scott, E. K. (2016). Functional profiles of visual-, auditory-, and water flow-responsive neurons in the zebrafish tectum. Current Biology, 26(6), 743-754.

Ca imaging with selective plane microscopy. Good refs on cell ensembles. They find ensembles that selectively encode stimulus features. PCA+promax, then clustering to identify them. Classification depends on threshold and manual elimination of "artifactual clusters", so not too objective. Inputs for each cluster tend to be in same laminae (layers). For moving bars, not much correlation with position, suggesting that it's not retinotopy, but true directionality. Most cells are unimodal (only 1-3% belong to two clusters).

Implications: Consider that there are many cells with different sensory / multisensory properties, so it is only to be expected that they would be tuned differently, and possibly via different mechanisms. Especially if they are starting to segregate into layers, as this would imply different distances from the soma to the dendrites and (potentially) the axon initial segment.